diff options
| author | Anton Vorontsov <anton.vorontsov@linaro.org> | 2012-02-24 05:14:46 +0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-03-12 12:31:25 -0700 |
| commit | 3516a8a4a77140b9039e3266c24eb5581066779d (patch) | |
| tree | cb8a53468120e702544108b93ec63dc143dbd7a5 | |
| parent | 6deb7d23c3d27520f4fb0b3a622966ba6760db71 (diff) | |
mm: memcg: Correct unregistring of events attached to the same eventfd
commit 371528caec553785c37f73fa3926ea0de84f986f upstream.
There is an issue when memcg unregisters events that were attached to
the same eventfd:
- On the first call mem_cgroup_usage_unregister_event() removes all
events attached to a given eventfd, and if there were no events left,
thresholds->primary would become NULL;
- Since there were several events registered, cgroups core will call
mem_cgroup_usage_unregister_event() again, but now kernel will oops,
as the function doesn't expect that threshold->primary may be NULL.
That's a good question whether mem_cgroup_usage_unregister_event()
should actually remove all events in one go, but nowadays it can't
do any better as cftype->unregister_event callback doesn't pass
any private event-associated cookie. So, let's fix the issue by
simply checking for threshold->primary.
FWIW, w/o the patch the following oops may be observed:
BUG: unable to handle kernel NULL pointer dereference at 0000000000000004
IP: [<ffffffff810be32c>] mem_cgroup_usage_unregister_event+0x9c/0x1f0
Pid: 574, comm: kworker/0:2 Not tainted 3.3.0-rc4+ #9 Bochs Bochs
RIP: 0010:[<ffffffff810be32c>] [<ffffffff810be32c>] mem_cgroup_usage_unregister_event+0x9c/0x1f0
RSP: 0018:ffff88001d0b9d60 EFLAGS: 00010246
Process kworker/0:2 (pid: 574, threadinfo ffff88001d0b8000, task ffff88001de91cc0)
Call Trace:
[<ffffffff8107092b>] cgroup_event_remove+0x2b/0x60
[<ffffffff8103db94>] process_one_work+0x174/0x450
[<ffffffff8103e413>] worker_thread+0x123/0x2d0
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | mm/memcontrol.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c index f538e9b824e..de67e916a96 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4502,6 +4502,9 @@ static void mem_cgroup_usage_unregister_event(struct cgroup *cgrp, */ BUG_ON(!thresholds); + if (!thresholds->primary) + goto unlock; + usage = mem_cgroup_usage(memcg, type == _MEMSWAP); /* Check if a threshold crossed before removing */ @@ -4550,7 +4553,7 @@ swap_buffers: /* To be sure that nobody uses thresholds */ synchronize_rcu(); - +unlock: mutex_unlock(&memcg->thresholds_lock); } |